1. Field of the Invention
This invention relates to a data processing system for efficiently processing data under a limited data transfer rate and/or a limited memory capacity, and more particularly to a data processing system for processing data supplied at a lower transfer rate from a data source such as an optical disc unit, to produce data in such a form as to be efficiently used by a device of a higher transfer rate such as a CRT display unit.
In recent years, optical discs such as compact discs have been developed and are extensively used as recording media for audio signals. In general, such an optical disc not only has a large memory capacity (for example, several megabytes per disc) but also is high in data transfer rate (for example, 150 kilobytes per second) and easy to handle. And therefore, an optical disc can also be used as a recording medium of other digital information, and is particularly suitable for use as recording means for an image processing unit.
Although a compact disc is superior in memory capacity and transfer rate, as described above, it has still been impossible for a compact disc to store data representative of an image whose pattern continuously varies over a long period of time.
As is well known, the transfer rate of data read from a compact disc is 150 kilobytes per second in the case of 60-minute recording type and 300 kilobytes per second in the case of 30-minute recording type. However, in order to display an image comparable in quality with those displayed on ordinary television sets, the data representative of the image must be fed to a display unit at a transfer rate more than a hundred times greater than the above-mentioned transfer rates of a compact disc. Thus, to display a motion image of a practical use in accordance with data read from a compact disc, the data necessarily be processed.
A series of images actually displayed on a display unit of, for example, a computer system may include a scene in which a motion of the image must be emphasized even at the sacrifice of a resolution of the image and may include a scene in which a resolution of the image must be enhanced even at the sacrifice of a motion of the image. Thus, display characteristics of an actual image such as a motion and a resolution generally vary in accordance with the lapse of time.